In a wireless communication system, a base station, situated at a fixed location, communicates with a plurality of wireless terminals, e.g., mobile nodes that may move throughout its cell. A given base station, with a single fixed antenna may have a fixed antenna pattern. Consider a single base station; its antenna pattern will support variable levels of channel quality between the base station and mobile nodes, depending on the mobile node's location with respect to the antenna pattern. Now consider that an adjacent base station, with its own antenna pattern, may be creating different levels of interference at different locations. The channel quality between the base station and a mobile node will vary as the mobile node moves to different locations within the cell. The mobile node may experience fading resulting in a degradations or loss of communication. Certain areas within the cell may be considered dead zones where the channel quality is too poor to establish communications. Methods and apparatus are needed that reduce fading and dead zones within cells.
In a system, with many mobile nodes, there will typically be a large diversity among the population of users, e.g., for any given antenna pattern there will be some users with good channel condition, some users with poor channel conditions, and other users with varying levels of channel conditions. At any given instant of time each mobile node experiences quasi-static channel conditions. Pilot signals may be broadcast to the mobile nodes; each mobile node's channel quality may be measured and reported back to the base station. Therefore, a base station could schedule mobile nodes with good channel quality, and hold-off scheduling mobile nodes with poor channel quality. When such a method is used in a strict manner, a mobile node, with poor channel quality, might have to move to a location with acceptable channel quality in order to be scheduled by the base station.
In another approach, the base station could periodically readjust its antenna pattern, again send pilot signals, wait for channel quality reports from the mobile node and schedule those mobile nodes with good channel quality. This second approach may lead to a long delay for a mobile node situated in a location of poor channel quality before the base station antenna pattern is adjusted to an acceptable level. In addition, this second approach favors one set of mobile nodes at the expense of another set of mobile nodes. The scheduling delays involved with either of these approaches may be unacceptable for certain types of delay-sensitive traffic such as voice. In some cases, if the traffic of the user has stringent delay constraints, the base station may, be forced to schedule a user even when channel conditions are not favorable resulting in a poor quality of service. Thus, for real time applications such as voice, it is often important to minimize the time period between transmission to a wireless terminal.
In cases where a channel's conditions are varied, practical constraints limit the rate at which the conditions in a particular channel may be varied without negatively impacting communications system performance. From a wireless terminal's perspective, rapid changes in a communications channel are difficult to track. Furthermore, rapid changes often result in a channel estimate used to decode a received signal being inaccurate since the channel conditions may have changed significantly since the channel measurements upon which the channel estimate is based were made. The use of feedback loops between a base station and a wireless terminal for power control and other purposes limits the rate at which communications channels can be varied since varying channel conditions at a rate faster than the rate at which channel condition information is measured by a wireless terminal and fed back to the base station can lead to the base station having largely inaccurate channel condition information.
In view of the above discussion, is should be appreciated that there is a need for improved methods and apparatus for supporting communication to multiple wireless terminals in a cell which may be distributed throughout the cell. Improved methods for providing a mobile with suitable channel conditions for receiving information from a base station are needed. From a scheduling perspective, it would be beneficial if the time interval between periods where a wireless terminal in a cell encounters good channel conditions could be minimized so that the wireless terminal need not have a long delay before encountering suitable transmission conditions. If intentional channel variations are used, it is desirable that the rate at which variations are introduced into a channel be slower than the rate at which channel measurements are made by the wireless terminals and/or the rate at which channel condition information is feed back to the base station. It would be desirable if at least some new methods address the problem of the relative duration of a mobile node's quasi-static channel condition relative to an acceptable scheduling latency. Methods and apparatus that address ways to mitigate interference effects from adjacent cells would also be beneficial. Methods that exploit the user diversity of the system, rather than be constrained by it, would also be beneficial. Such improved methods could increase user satisfaction, increase quality of service, increase efficiency, and/or increase throughput.